Control Protocol of Finite Dimensional Quantum Systems

An analytic control protocol of two types of finite dimensional quantum systems is proposed. The system can be driven to an arbitrary target state using cosine classical fields in finite cycles. The control parameters which are time periods of interaction between systems and control fields in each cycle are connected with the probability amplitudes of target states via trigonometrical functions and can be determined analytically.     

少周期非均匀场下原子空间位置对高次谐波发射的影响

本文通过数值求解含时薛定谔方程,研究了少周期非均匀激光脉冲作用下氦原子选取不同的空间位置时高次谐波的发射情况.通过对原子在纳米结构空隙中心附近区域不同空间位置上的高次谐波发射情况的研究发现,非均匀激光场中,即使原子处在中心附近的很小的区域内,原子的空间位置也直接影响着高次谐波发射.随着空间内原子坐标的增大,高次谐波的截止得到扩展,且谐波平台区并非单向扩展,而是向两端同时的扩展.通过时频分析和半经典三步模型研究了高次谐波发射的物理机制,并对获得的物理现象给出合理的解释.     

Principle of Symmetric Bracket Invariance as the Origin of First and Second Quantization

The principle of invariance of the c-number symmetric bracket is used to derive both the quantum operator commutator relation and the time-dependent Schrödinger equation. A c-number dynamical equation is found, which leads to the second quantized field theory of bosons and fermions.     

THE CAUSAL INTERPRETATION OF QUANTUM FIELDS AND THE VACUUM

We consider some conceptual aspects of the causal interpretation of quantum fields as it applies to the vacuum. We will contrast this with the view of the vacuum according to Bohr's principle of complementarity.     

基于提高精度的量子雷达方案及其进展

定位测量一直是人们关注的问题,将量子技术应用于定位任务有望展示出经典定位方案无法达到的优势。目前,已有部分量子雷达方案被提出,展示了科研工作者从量子信息角度对定位测量的新思考。本文总结了部分已有的量子雷达方案,介绍了相关方案的概念和分类,并着重对量子定位、量子照明和三维增强雷达三种方案的基本原理进行论述,同时分析了各方案的优势以及亟待解决的问题。     

A Three-Stage Quantum Cryptography Protocol

We present a three-stage quantum cryptographic protocol based on public key cryptography in which each party uses its own secret key. Unlike the BB84 protocol, where the qubits are transmitted in only one direction and classical information exchanged thereafter, the communication in the proposed protocol remains quantum in each stage. A related system of key distribution is also described.     

The Lorentz force and energy-momentum for off-shell electromagnetism

The kinematics of pre-Maxwell electrodynamics is examined and interpretations of these fields is found through an examination of the associated Lorentz force and the structure of the energy-momentum tensor.     

量子密钥分发与量子安全直接通信

量子通信具有高安全性等优点,是当前的国际研究前沿,量子安全直接通信和量子密钥分发是两种重要的量子信息方式.量子密钥分发通过量子信道产生随机的密钥,而量子安全直接通信直接在量子信道中传输秘密信息.本文力图利用浅显易懂的语言介绍量子安全直接通信和量子密钥分发的基本原理;重点描述几个典型的量子安全直接通信方案,介绍目前的发展状态并展望未来.     

Eavesdropping on the＇ping-pong＇ quantum communication protocol freely in a noise channel

We introduce an attack scheme for eavesdropping freely the ping-pongquantum communication protocol proposed by Bostr\"{o} m and Felbinger[Phys. Rev. Lett. 89, 187902 (2002)] in a noise channel.The vicious eavesdropper, Eve, intercepts and measures the travelphoton transmitted between the sender and the receiver. Then shereplaces the quantum signal with a multi-photon signal in the samestate, and measures the returned photons with the measuring basis,with which Eve prepares the fake signal except for one photon. Thisattack increases neither the quantum channel losses nor the errorrate in the sampling instances for eavesdropping check. It works foreavesdropping the secret message transmitted with the ping-pongprotocol. Finally, we propose a way for improving the security ofthe ping-pong protocol.     

A Kinetic Theory Approach to Quantum Gravity

We describe a kinetic theory approach to quantum gravity by which we mean a theory of the microscopic structure of space-time, not a theory obtained by quantizing general relativity. A figurative conception of this program is like building a ladder with two knotty poles: quantum matter field on the right and space-time on the left. Each rung connecting the corresponding knots represents a distinct level of structure. The lowest rung is hydrodynamics and general relativity; the next rung is semiclassical gravity, with the expectation value of quantum fields acting as source in the semiclassical Einstein equation. We recall how ideas from the statistical mechanics of interacting quantum fields helped us identify the existence of noise in the matter field and its effect on metric fluctuations, leading to the establishment of the third rung: stochastic gravity, described by the Einstein–Langevin equation. Our pathway from stochastic to quantum gravity is via the correlation hierarchy of noise and induced metric fluctuations. Three essential tasks beckon: (1) deduce the correlations of metric fluctuations from correlation noise in the matter field; (2) reconstituting quantum coherence—this is the reverse of decoherence—from these correlation functions; and (3) use the Boltzmann–Langevin equations to identify distinct collective variables depicting recognizable metastable structures in the kinetic and hydrodynamic regimes of quantum matter fields and how they demand of their corresponding space-time counterparts. This will give us a hierarchy of generalized stochastic equations—call them the Boltzmann–Einstein hierarchy of quantum gravity—for each level of space-time structure, from the the macroscopic (general relativity) through the mesoscopic (stochastic gravity) to the microscopic (quantum gravity).     

Binding energy of a hydrogen-like donor impurity in a quantum well-wire in magnetic and electric fields

The effect of a longitudinal magnetic and a transverse electric fields on the binding energy of a hydrogen-like donor impurity is studied for a semiconductor quantum well-wire approximated by a cylindrical well of finite depth. It is shown that the magnetic and electric fields as well as the impurity distance from the wire axis are the effective tools for the influence on the binding energy.     

Barrier Li Quantum Dots in Magnetic Fields

The methods for the few-body system are introduced to investigate the states of the barrier Li quantumdots (QDs) in an arbitrary strength of magnetic field. The configuration, which consists of a positive ion located on thez-axis at a distance d from the two-dimensional QD plane (the x-y plane) and three electrons in the dot plane boundby the positive ion, is called a barrier Li center. The system, which consists of three electrons in the dot plane bound bythe ion, is called a barrier Li QD. The dependence of energy of the state of the barrier Li QD on an external magneticfield B and the distance d is obtained. The angular momentum L of the ground states is found to jump not only withthe variation of B but also with d.     

安全传送明文的量子直传实验方案设计

乒乓直传协议是一种新颖的量子直传通信协议。基于量子纠缠特性,乒乓协议允许绝对安全地进行明文直接通信和渐进地进行密钥安全分发。是一种绝对安全的即时通信协议。该量子直传协议将来有望成为安全稳定的光量子通信的主流方式。然而,目前还没有该协议的物理实现方案。分析了乒乓直传协议的工作原理．给出了该协议的流程图,进而分析了协议的物理实现机制,结合纠缠光子源、自由空间单光子路由控制和单光子检测技术,提出了在自由空间中实现乒乓直传协议的实验技术方案,并设计出了乒乓直传协议的实验装置。此实验技术方案为从实验角度进一步研究乒乓协议,以及未来此协议的商业化应用提供了参考。